As a pressing force sensor related to the present invention, there is exemplified a sensor described in Japanese Laid-Open Patent Publication. No. 2000-275114 (Patent Document 1). Patent Document 1 describes, for example, a pressing force sensor equipped with a piezoelectric element in which a piezoelectric crystal thin film is formed on each of both principal surfaces of a flexible substrate made of a metal thin plate, and electrode layers are formed on the piezoelectric crystal thin films. The electrode layers of the piezoelectric element are connected to an external circuit through electrode films disposed such that the piezoelectric element is held therebetween.
Patent Document 1 also describes an embodiment in which an electrode film also serves as a protective film. In the embodiment, there is used as the electrode film a film made of polyethylene terephthalate (PET) on which electrode patterns made of copper foil are formed, for example.
However, in the pressing force sensor described in Patent Document 1, if a solder reflow process is used to connect the sensor to an external circuit, heat resistance is problematic specifically with the electrode film. As described above, an electrode film made of, for example, PET cannot withstand solder reflow temperatures (260° C. or higher).
In order to address this issue, there can be considered, for example, a countermeasure in which a flexible printed circuit board is separately prepared for connection to an external circuit, and the flexible printed circuit board is connected to the electrode film through an anisotropic conductive film or an anisotropic conductive adhesive. However, this countermeasure requires high production cost.